1. Field of the Invention
The present invention relates to a method of producing an olefin oxide. More particularly, the present invention relates to a method of producing an .alpha.-olefin oxide, with an excellent selectivity.
The .alpha.-olefin oxides are industrial materials very useful for various surfactants and polymer-modifying agents.
2. Description of the Related Arts
It is well known that olefin compounds can be converted to corresponding epoxide compounds by a reaction with organic peracid, and in a well known method, the organic peracid is selected from perbenzoic acid and perphthalic acid. In the industrial production of the olefin oxide, however, this method is disadvantageous in that the specific peracid must be synthesized from a corresponding starting acid, and after the oxidation reaction, the resultant acid compound must be recovered by an expensive process.
Also, it is known from D. Swern et al., J. Am. Chem. Soc., 68, 1504 (1964) that .alpha.-olefin oxide is synthesized by using a solution of peracetic acid in acetic acid.
In the industrial production of the .alpha.-olefin oxide, this method is disadvantageous in that, in the preparation of the peracetic acid solution, a very high concentration of 90% or more of hydrogen peroxide must be employed, and since the oxidation reaction is carried out in a homogeneous reaction system, the resultant .alpha.-olefin epoxide must be extracted by adding a large amount of water to the resultant reaction mixture.
To remove the above-mentioned disadvantages, a new method is known in which an olefin is epoxidized with an oxidant mixture of hydrogen peroxide with a carboxylic acid, for example, acetic acid, in the presence of an acid catalyst, for example, a mineral acid, while generating an organic peracid, for example, peracetic acid, from the hydrogen peroxide and carboxylic acid. This method is referred to as an in-situ method, and is now most widely used as the epoxidizing method.
This in-situ method for the production of olefin oxide is advantageous in that the starting olefin can be satisfactorily epoxidized by using the carboxylic acid, for example, acetic acid, in a relatively small amount of about 50 molar% based on the molar amount of the starting olefin, and this epoxidation can be easily effected in a simple reactor. Therefore, this in-situ method is advantageously utilized to epoxidize an unsaturated compound having a di-substituted double bond, for example, a vegetable oil.
Nevertheless, .alpha.-olefin, which is a monosubstituted olefin, exhibits a low reactivity. For example, in D. Swern, "Organic Peroxides", Vol. 1 (1970) Wiley-Interscience, it is mentioned that an olefin having one alkyl substituent, namely an .alpha.-olefin, exhibits a reactivity corresponding to about 1/22.5 of that of an olefin having two alkyl substituents.
Also, this in-situ method is disadvantageous in that undesirable side reactions, for example, a cleavage reaction of the epoxy ring structure of the resultant olefin epoxide, occur.
To prevent the undesirable side reactions caused by the use of the in-situ method, usually an organic solvent is added to the reaction mixture.
For example, Japanese Unexamined Patent Publication No. 57-145,866 discloses the employment of benzene as an organic solvent; German Patent No. 1,568,016 teaches the use of benzene or toluene; and Japanese Unexamined Patent Publication No. 51-36,448 provides the use of a chlorine-containing organic solvent, for example, chloroform.
Nevertheless, the use of the above-mentioned organic solvents is dangerous, in that benzene is a harmful substance specified by the Labor Safety and Hygiene Law and must be carefully handled. Toluene is also a harmful substance in that it is easily charged with static electricity, and thus there are many reports of fires due to a self-combustion of toluene. Especially, in the epoxidization of the .alpha.-olefin with hydrogen peroxide in the presence of toluene, a large amount of heat is generated and oxygen gas is also produced, and thus the use of toluene causes the .alpha.-olefin epoxidizing reaction to be very dangerous in that fires often occur.
Further, the chlorine-containing organic solvents per se are harmful to the human body, and can generate a harmful gas, for example, phosgene or a hydrogen chloride gas by the occurrence of a fire. Also, recently, the chlorine-containing organic solvents have been designated as a pollutant of the global environment, in that they lead to a destruction of the ozonosphere.
In the conventional methods, such dangerous organic solvents are often used from the viewpoint of productivity, but improvements in the quality of the working environment and in safety are now considered more important than productivity.
Furthermore, the use of the organic solvent causes a deterioration in the quality of the resultant product, due to a small amount of residual solvent in the product. Accordingly, in view of the above-mentioned disadvantages, there is an urgent need for a new method of epoxidizing an olefin, without employing an organic solvent, by an in-situ method.
Still furthermore, a selectivity of reaction is highly contributory to a degree of separation between an oil phase and an aqueous phase in a washing step for a reaction product. When the selectivity of reaction is low, the resultant reaction product is emulsified in the washing step and this emulsification causes the reaction product to be useless. In other words, even if the reaction per se is carried out smoothly, if the reaction product cannot be smoothly separated from the reaction system by the washing procedure, this reaction process is considered incomplete.